Occasionally my iMac, running OS 10.3.7 and Mail 1.3.9, announces loudly: "Mail is in."
In Mail preferences, the new mail sound is set to "none." This happens rarely--it may go several weeks without doing it, then it speaks up again. I don't know where it could be coming from; mail preferences does not even list a voice saying "mail is in" as one of the options.
This morning it frightened my wife who heard the voice and thought someone was in the house. Does anyone have any idea why this is happening or how to stop it (other than muting the sound every time I leave the computer)?